1. Field of the Invention
This invention generally relates to an apparatus and method for ultrasonically bonding a web, and more specifically relates to an improved apparatus and method wherein ultrasonic bonding dwell time on a moving material is not limited by the speed of the moving material relative to a stationary bonding station.
2. Description of Related Art
U.S. Pat. No. 4,193,833 to J. L. Young discloses the sealing of thermoplastic-coated paperboard cartons in which the carton layers are engaged on opposite surfaces by, respectively, a vibrating horn and an anvil, for a time sufficient to activate the thermoplastic sealant material. The anvil is movable with respect to the horn, between an inactive position (retracted), and an active position (engaged) in which the opposed work surfaces of the horn and anvil engage the carton layers in a clamping relationship while the horn is energized.
Federal Republic of Germany Offenlegungsschrift No. 1,632,007 of W. Pechmann, published Aug. 20, 1970, discloses a device comprising a plurality of ultrasonic horns and corresponding anvils mounted about the periphery of a rotating head member. During rotation of the head member, a paired anvil/horn unit applies a clamping pressure on a discrete thermoplastic workpiece for a particular period of time and then retracts the horn and anvil for release of the bonded workpiece at another location.
U.S. Pat. No. 4,490,199 to F. G. Dunning discloses an apparatus and method for splicing polymeric webs supported on an anvil, wherein an ultrasonic spot welder is slidably connected to support bars by bearing assemblies and is translated by a driving screw in a direction transverse of the web (column 5, line 68 to column 6, line 4) or axially of the web (column 4, line 66 to column 5, line 1). The welding horn is extended toward the web by a retraction cylinder assembly.
Generally, ultrasonic bonding systems are known in which a sonotrode and its anvil are respectively reciprocated or rotated to meet on opposite sides of a moving continuous web to momentarily clamp the moving web between their respective bonding surfaces to ultrasonically bond it. It is known to mount a plurality of sonotrodes and cooperating anvils along the peripheries of respective counter-rotating drums positioned to form between the bonding surfaces thereof a nip through which one or more plies of moving web are passed. As the drums rotate, portions of the web or webs are clamped between the respective paired bonding surfaces as they pass through the nip in opposed, facing alignment with each other, on opposite sides of the web. With this arrangement, the dwell time of the paired bonding surfaces in bonding-effective alignment with each other is necessarily limited by the speed of travel of the web, which determines the peripheral linear speed of the drums.